Fruit Antioxidant Properties of "Costata" Persimmon (Diospyros kaki Thunb.) under Different Astringency Removal Treatments

This study evaluated alternative postharvest de-astringency treatments for ‘Costata’ persimmon (Diospyros kaki Thunb) fruits to assess total phenols, soluble tannins, carotenoids, vitamin C, and antioxidant activity (reducing power, total antioxidant capacity, and DPPH scavenging) during the shelf life. Experiments were conducted in the 2023 and 2024 seasons using six treatments and a control: distilled water (Tc), calcium carbide (CaC₂) (T1), potassium carbonate (K₂CO₃) at 2.5% (T2) and 5% (T3), sodium bicarbonate (NaHCO₃) at 2.5% (T4) and 5% (T5), and 40% ethanol (T6). Results indicated that all antioxidant parameters declined progressively during the shelf-life period, but the rate of decline was significantly affected by the postharvest treatments. Fruits treated with CaC₂ showed rapid de-astringency but exhibited the lowest retention of total phenols, vitamin C, and antioxidant capacity, reflecting accelerated ripening and oxidative degradation. On the other hand, fruits treated with NaHCO₃ and K₂CO₃ showed a progressive loss of antioxidant compounds over the course of their shelf life, but they retained higher levels of carotenoids, polyphenols, and radical scavenging activity. Ethanol treatment also delayed antioxidant depletion but was less effective than carbonate treatments. These results validate the use of alkaline treatments, specifically K₂CO₃ at 2.5%, as safe and environmentally beneficial substitutes for CaC₂ in the simultaneous elimination of astringency and maintenance of antioxidant quality in "Costata" persimmon fruits.